Control arrangement for an hydraulic assist turbocharger

ABSTRACT

A control arrangement is provided for controlling the operation of an hydraulic assist turbocharger of the type including an hydraulic turbine driven by an hydraulic fluid under pressure to supplementally drive a turbocharger during engine operating conditions when supplemental air flow is required. The control arrangement includes a dual function control valve responsive to engine speed and load to regulate the supply of hydraulic fluid to the hydraulic turbine in accordance with engine air flow requirements.

BACKGROUND OF THE INVENTION

This invention relates generally to turbocharger systems for use withcombustion engines. More specifically, this invention relates to acontrol arrangement particularly for use in controlling the operation ofan hydraulic assist turbocharger such as that described in commonlyassigned U.S. Pat. No. 4,285,200.

Turbochargers and turbocharger systems in general are known for use insupplying a combustion engine with a charge of air under pressure,commonly referred to as charge air. The turbocharger typically comprisesa turbine wheel and a compressor wheel mounted for rotation with acommon shaft. The turbine wheel and the compressor wheel are positionedwithin turbine and compressor housings, respectively, which are in turnsecured to a so-called center housing including appropriate shaftbearings for supporting the rotating shaft. Exhaust gases from acombustion engine are coupled for passage through the turbine housing torotatably drive the turbine wheel, whereby the rotating turbine wheelcorrespondingly drives the compressor wheel to compress ambient air forsupply as charge air to the air intake of the engine.

Turbocharged engines are highly advantageous when compared withconventional naturally-aspirated engines in that substantially denserair is delivered to the combustion chamber or cylinders of the engine.This increased air density results in an increased mass flow ofavailable air for combustion to enable the engine to operate atsubstantially higher performance levels and with greater efficiency.However, an inherent limitation with turbochargers has been theirinability to provide the engine with sufficient charge air during someconditions of engine operation. For example, charge air supplied to theengine by the turbocharger during low speed operating conditionstypically is insufficient to permit engine operation at a relativelyhigh load and/or to permit relatively rapid engine acceleration.Moreover, in a two cycle engine, charge air supplied by the turbochargerduring starting and/or during other low speed operating conditionsnormally is insufficient to keep the engine from stalling.

A variety of system concepts are known in the art for boosting orsupplementing the normal charge air output of a turbocharger duringselected engine operating conditions. For example, auxiliary combustionsystems have been proposed wherein the energy level of the engineexhaust gases is supplemented during selected engine operatingconditions. Compound turbocharger systems have also been proposedwherein multiple turbine and/or compressor components are coupledtogether to provide supplemental charge air. Additional system conceptsinclude, for example, mechanical drive trains for mechanicallysupplementing turbocharger rotation and hydraulic drive systems forhydraulically supplementing turbocharger rotation.

One system concept of particular note is described in detail in U.S.Pat. No. 4,285,200 and comprises a specific hydraulic drive arrangementin the form of a so-called three wheel turbocharger. In this system, anonventilated hydraulic turbine is carried on a turbocharger shaftbetween the turbine and compressor wheels, and this nonventilatedhydraulic turbine is supplied with hydraulic fluid under pressure tosupplementally drive the turbocharger. In this manner, the mass flowoutput of charge air for supply to the engine is significantly increasedduring selected operating conditions. However, successful operation ofthis type of hydraulic drive system is predicated upon the provision ofan efficient control arrangement for rapidly supplying the hydraulicturbine with a regulated flow of pressurized hydraulic fluid wherein thefluid flow rate is scheduled in accordance with engine air flowrequirements to provide the requisite supplemental driving of theturbocharger. Moreover, it is highly desirable for the controlarrangement to unload hydraulic pumping elements when supplementaldriving is not required or the need for supplemental driving is reducedsuch that parasitic hydraulic power losses are minimized.

The present invention provides a control arrangement particularlydesigned to provide a regulated flow of pressurized hydraulic fluid tothe hydraulic turbine of an hydraulic assist turbocharger, wherein thefluid flow rate is controlled in response to engine speed and load andwherein the control arrangement substantially unloads hydraulic pumpingelements from the engine when the need for supplemental turbochargerdriving is reduced.

SUMMARY OF THE INVENTION

In accordance with the invention, a control arrangement is provided forcontrolling the flow of pressurized hydraulic fluid to an hydraulicassist turbocharger to supplementally drive the turbocharger forsupplying charge air to a combustion engine. The hydraulic assistturbocharger includes a turbine wheel and a compressor wheel mounted ona common shaft and respectively received within turbine and compressorhousings. Exhaust gases from the combustion engine drive the turbinewheel which correspondingly drives the compressor wheel to supplyrelatively high density charge air to the engine. An hydraulic turbineis coupled to the turbocharger shaft, and this hydraulic turbine isselectively supplied with pressurized hydraulic fluid, such as oil, tosupplementally drive the turbocharger during selected engine operatingconditions and thereby provide supplemental charge air to the engine.The control arrangement of this invention includes hydraulic pumpingelements for supplying the pressurized hydraulic fluid to the hydraulicturbine, together with a dual function control valve responsivesimultaneously to engine speed and engine load to control the flow rateof the pressurized hydraulic fluid to the hydraulic turbine and therebycontrol the relative degree of supplemental turbocharger driving inaccordance with engine air flow requirements.

In accordance with one form of the invention, the hydraulic assistturbocharger comprises a so-called three wheel turbocharger having anonventilated hydraulic turbine mounted on the turbocharger shaftbetween the turbine and compressor wheels. When supplemental driving ofthe turbocharger is required, such as during low speed full load engineoperating conditions or during low speed acceleration engine operatingconditions, the hydraulic fluid is supplied under pressure to thenonventilated hydraulic turbine to rotatably drive the hydraulic turbineand thereby supplementally drive the turbocharger.

In a preferred form, the control arrangement comprises a pair ofpositive displacement gear pumps driven by the engine to supply paralleloutputs of pressurized hydraulic fluid having a flow rate directlyproportional to engine speed. These parallel fluid outputs are combinedfor supply as a single, pressurized fluid flow for driving thenonventilated hydraulic turbine. The control valve responds to increasesin engine speed and engine load to progressively disconnect or unloadthe fluid output of one gear pump and then to progressively unload thefluid output of the other gear pump as engine speed and/or loadincreases and the requirement for supplemental turbocharger driving isreduced. The fluid outputs, when disconnected from the hydraulicturbine, are coupled to a relatively low pressure sump such that one orboth of the gear pumps are substantially unloaded to minimize parasitichydraulic power losses.

The control valve comprises a pressure regulating spool valve having apair of spool lands movable together within a valve body to unload aportion of the gear pump fluid output to maintain the pressure of thehydraulic fluid supplied to the hydraulic turbine relatively constantthroughout a range of engine speeds. An engine speed increases resultingin a corresponding increase in the flow rates of the gear pump fluidoutputs, the spool lands move within the valve body to progressivelydisconnect and unload the fluid output of one gear pump and then to atleast partially unload the fluid output of the other gear pump. Theunloaded fluid outputs are coupled to a relatively low pressure sump tominimize power requirements for continued driving of the gear pumps.

The spool valve is further responsive to the pressure of the charge airsupplied to the engine, wherein the charge air pressure is indicative ofengine load. The charge air acts against a flexible diaphragm whichmovably positions an actuator rod into engagement with the spool valveto move the spool lands toward a position further unloading the gearpump fluid outputs as engine load increases. When a predeterminedrelatively high engine load is reached, the spool lands are moved to aposition substantially completely unloading the fluid outputs of both ofthe gear pumps. When this occurs, a portion of one fluid output iscoupled to an hydraulically actuated shut-off valve at the upstream sideof the hydraulic turbine to positively stop flow of hydraulic fluid tothe hydraulic turbine.

In a modified form of the invention, a transient responsive overridevalve is provided for selectively supplying a portion of one fluidoutput to an override chamber within the spool valve for urging thespool lands toward a position of reduced unloading of the fluid outputsfor the duration of a transient condition, such as heavy acceleration.When this occurs, the reduced fluid output unloading increases thepressure of the fluid supplied to the hydraulic turbine tocorrespondingly increase the supplemental driving of the turbochargerduring the transient condition.

Other features and advantages of the present invention will become moreapparent from the following description, taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a schematic diagram illustrating an hydraulic assistturbocharger and engine system including a control arrangement embodyingthe novel features of the invention;

FIG. 2 is an enlarged vertical section somewhat in schematic formillustrating a hydropneumatic control valve forming a portion of thecontrol arrangement;

FIG. 3 is an enlarged vertical section somewhat in schematic formillustrating a shut-off valve forming a portion of the controlarrangement;

FIG. 4 is a graphic representation depicting the operation of thecontrol arrangement of this invention; and

FIG. 5 is an enlarged vertical section somewhat in schematic form of ahydropneumatic control valve similar to FIG. 2 in conjunction with analternative form of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A turbocharged engine system is illustrated generally in FIG. 1 and isdesignated by the reference numeral 10. As shown, the engine system 10includes an hydraulic assist turbocharger 12 for supplying relativelyhigh density charge air to a combustion engine 14, such as a two-cycleor a four-cycle internal combustion engine. The turbocharger 12 isnormally driven in a conventional manner by exhaust gases expelled fromthe engine. However, during selected conditions of engine operation, theturbocharger is supplementally driven by hydraulic fluid under pressurewhich is supplied and regulated by a control arrangement 16 of thisinvention.

The hydraulic assist turbocharger 12 comprises, in accordance with apreferred form of the invention, a so-called three wheel turbocharger ofthe type described in detail in commonly assigned U.S. Pat. No.4,285,200. The turbocharger 12 thus includes a turbine wheel 18 and acompressor wheel 20 connected to the opposite ends of a common shaft 30and received respectively within turbine and compressor housings 22 and24. The turbine and compressor housings 22 and 24 are interconnected bya center housing 26 including bearings 28, such as suitable journal andthrust bearings, for rotatably supporting the shaft 30, all in awell-known manner.

The turbocharger turbine wheel 18 is rotatably driven by exhaust gasesexpelled from the engine 14 through an exhaust gas manifold 32 and anexhaust conduit 34. The rotating turbine wheel 18 rotatably drives theturbocharger shaft 30 and the compressor wheel 20 whereby the compressorwheel 20 draws in and compresses ambient air. This compressed ambientair comprises so-called boost or charge air and is supplied to theengine 14 via a charge air conduit 36 to an air intake manifold 38.Conveniently, as shown, a charge air cooler heat exchanger 40 ofconventional design may be provided along the conduit 36 to cool thecompressed charge air so as to reduce the total engine heat load and tofurther densify the charge air. This relatively high density charge airsupplied to the engine enables the engine to operate at a relativelyhigh performance and efficiency level.

The engine 14 conventionally includes an hydraulic pumping system 42 forproviding a lubricant, such as motor oil, to the engine and to theturbocharger 12 for lubrication purposes. More specifically, the pumpingsystem 42 normally includes a main oil sump 44 from which oil is pumpedby a relatively low pressure engine-driven oil pump 46 to the engine andthe turbocharger. As shown, the oil is pumped through an oil filter 48and an oil cooler 50 and further through an appropriate network ofpassages as indicated by a conduit 52 to engine components requiringlubrication. The oil is also coupled through an oil supply conduit 54 tothe center housing 26 of the turbocharger 12 for lubrication of theturbocharger bearings 28 via a network of appropriate passages indicatedby the conduits 55 which can be partially or wholly formed within thecenter housing. The oil passes through the bearings 28, typically as bya gravity-drain system, and is returned to the sump 44 by an oil returnconduit 56. Accordingly, the turbocharger bearings 28 share the enginehydraulic system 42 to assure proper bearing lubrication for allconditions of engine operation.

During some conditions of engine operation, the engine exhaust gaseshave insufficient energy for driving the turbocharger at a rotationalspeed necessary to provide sufficient mass flow of charge air to theengine for maintaining desired engine performance levels. Such operatingconditions may include, for example, relatively low speed operationwherein the exhaust gas energy level is inadequate to permit operationat a relatively high load or with a relatively rapid acceleration.Moreover, in a two-cycle engine, the turbocharger is incapable ofproviding sufficient charge air during engine cranking speeds to permitstarting of the engine or to properly scavenge the engine cylinders ofexhaust products during low speed operation. Accordingly, to assure thatthe turbocharger is driven at a sufficient speed to supply the enginewith a sufficient quantity of charge air at all times, the three wheelturbocharger 12 includes a nonventilated hydraulic turbine 58 for use insupplementally driving the turbocharger.

As illustrated, the nonventilated hydraulic turbine 58 is mounted withinthe turbocharger center housing 26 upon the turbocharger shaft 30 andaxially between the sets of bearings 28. When supplemental driving ofthe turbocharger is required, a relatively high pressure hydraulicfluid, such as oil shared from the engine oil system 42, is provided tothe center housing 26 by a high pressure pump assembly 60 forming aportion of the control arrangement 16 of this invention to be describedin more detail. The pressurized fluid is coupled to the center housingthrough a supply conduit 62 for flow into driving communication with thehydraulic turbine 58 to supplementally drive the turbocharger andthereby increase the mass flow of charge air to the engine.

The general construction and operation of the nonventilated hydraulicturbine 58 is described in detail in the above-referenced U.S. Pat. No.4,285,200, which is incorporated by reference herein. Importantly, thepressurized hydraulic fluid rotatably drives the hydraulic turbine 58and the turbocharger shaft 30 at a relatively high rotational speed toresult in a corresponding rotation of the compressor wheel 20 toincrease the mass flow of charge air supplied to the engine. Thehydraulic fluid is then discharged from the center housing 26 into adischarge conduit 64 for flow through a one-way check valve 66 into theoil supply conduit 54 and return therethrough to the intake side of thehigh pressure pump assembly 60. Conveniently, while the fluid flowthrough this oil supply conduit 54 is thus reversed throughout theduration of supplemental driving of the turbocharger, sufficientback-pressure remains in the conduit 54 to insure sufficient oil flow tothe turbocharger bearings 28 and return via the oil return conduit 56.The check valve 66 functions to prevent flow of fluid from the oilsupply conduit 54 into communication with the hydraulic turbine 58 whensupplemental turbocharger driving is not required.

The control arrangement 16 of this invention is provided for closelycontrolling the supply of the hydraulic fluid to the nonventilatedhydraulic turbine whenever supplemental turbocharger driving isrequired. More particularly, the control arrangement 16 is responsive toa combination of engine speed and engine load to provide a relativelyhigh degree of supplemental driving of the turbocharger when enginespeed and load are relatively low. However, as engine speed and/or loadincreases, the energy level of the engine exhaust gases correspondinglyincreases such that the relative need for supplemental turbochargerdriving progressively decreases. In this regard, the control arrangement16 regulates the supply of the pressurized hydraulic fluid in responseto increases in engine speed and/or load to reduce the relative degreeof supplemental driving of the turbocharger. Accordingly, the controlarrangement constitutes an energy efficient system which provides onlythe degree of supplemental turbocharger driving required to maintain thedesired charge air flow. Importantly, as the relative need forsupplemental turbocharger driving decreases, the control arrangement 16advantageously unloads portions of the high pressure pump assembly 60 tominimize the amount of engine power used to operate the pump assembly.

In general terms, the control arrangement 16 comprises a plurality ofpositive displacement pumping elements which form the high pressure pumpassembly 60 and which provide individual hydraulic flow outputs forconnection and supply as a combined pressurized hydraulic flow throughthe supply conduit 62 to the nonventilated hydraulic turbine 58. A dualfunction hydropneumatic control valve 76 is associated with theindividual hydraulic flow outputs and operates to progressivelydisconnect the hydraulic flow outputs one at a time from the hydraulicturbine 58 in response to a combined function of increasing engine speedand load. The control valve 76 couples the individual flow outputs oneat a time to an appropriate low pressure portion of the system such thatthe positive displacement pumping elements are substantially unloaded.Thus, driving energy required to operate the unloaded pumping elementsis minimized, whereby the unloaded elements can be continuously drivenin an energy-efficient manner with low power consumption such that theirfluid outputs are substantially immediately available for subsequentsupplemental driving of the turbocharger when engine speed and/or loadis subsequently reduced.

In a preferred form of the invention, as illustrated in FIG. 1, thepositive displacement pumping elements of the high pressure pumpassembly 60 comprise a pair of positive displacement gear pumps 68 and70 having their intakes coupled in common to a relatively small sump 69at the discharge side of the low pressure oil pump 46. These gear pumps68 and 70, which can be provided in any suitable number, are preferablyformed as part of a single gear pump unit or assembly driven by theengine as by a suitable mechanical connection to the engine camshaft(not shown) or the like. Accordingly, the two gear pumps 68 and 70provide separate hydraulic flow outputs each having a flow rate directlyproportional to engine speed.

The separate hydraulic flow outputs of the gear pumps 68 and 70 flowthrough a pair of parallel flow conduits 72 and 74 which are coupled tothe dual function control valve 76. When engine speed and load arerelatively low, the control valve 76 permits the flow output from thegear pump 68 to flow through a branch conduit 78 and a one-way checkvalve 80 into a portion 74' of the flow conduit 74 whereby the flowoutputs of the two gear pumps 68 and 70 are combined into a singlehydraulic flow.

The combined hydraulic flow in the conduit 74 is coupled to an inletport 81 of a relatively low pressure hydraulic shut-off valve 82 whichpermits passage of the hydraulic fluid into the supply conduit 62. Moreparticularly, as viewed in FIG. 3, the shut-off valve 82 comprises ahollow valve body 84 containing a valve piston 86 biased by a relativelylightweight spring 88 to move a valve plug 90 of relatively small crosssection toward normal seated engagement upon an annular valve seat 92 toclose the inlet port 81. However, the pressure of the hydraulic fluid atthe valve inlet 81 causes the valve plug 90 and the piston 86 to move tothe open position, as shown in FIG. 3, to permit fluid flow through theinlet port 81 into the valve body 84 and further through an outlet port85 to the supply conduit 62. As described hereinabove, this supplyconduit 62 couples the pressurized hydraulic fluid flow to thenonventilated hydraulic turbine 58 for supplemental driving of theturbocharger.

The dual function control valve 76 controls the supply of hydraulicfluid through the conduit 62 to the hydraulic turbine 58 byprogressively unloading the flow outputs of the gear pumps 68 and 70 inresponse to increases in engine speed and/or load. The control valve 76is, in the illustrated embodiment, responsive primarily to variations inengine speed to maintain the hydraulic pressure in the conduit 62 at asubstantially constant level throughout a range of engine operatingspeed. In this manner, the energy input to the hydraulic turbine issubstantially constant throughout this engine speed range tosupplementally drive the turbocharger compressor. However, since thedriving energy in the exhaust gases also increases with engine speed,the relative proportion of the total driving energy supplied by thehydraulic fluid decreases progressively with increases in engine speed.This relative decrease in supplemental turbocharger driving isconsistent with a reduced need for supplemental driving at higher enginespeeds.

The dual function control valve 76 is further responsive to engine loadto partially or completely override the normal speed-responsiveoperation. More particularly, when engine load increases to a relativelyhigh level, the available energy in the engine exhaust gases for drivingthe turbocharger turbine 18 correspondingly increases such that the needfor supplemental turbocharger driving is reduced or eliminated. When ahigh load condition occurs, the control valve 76 functions to furtherunload the flow outputs of the gear pumps 68 and 70 to reduce thehydraulic pressure in the supply conduit 62 and thereby reduce thedegree of supplemental driving of the turbocharger. If the engine loadis sufficiently high and no supplemental turbocharger driving required,the control valve 76 functions to unload the pump flow outputscompletely whereupon turbocharger operation continues solely in responseto engine exhaust gases. When the engine load subsequently returns to alower level, the control valve 76 progressively reconnects the pump flowoutputs to the supply conduit 62 to correspondingly return to a normalspeed-responsive mode.

As shown in detail in FIG. 2, the control valve 76 comprises a spoolvalve having a pair of spool lands 94 and 95 movable within an elongatedhollow valve body 96 for respectively coupling the hydraulic flowoutputs of the gear pumps 68 and 70 to a pair of outlet conduits 97 and98. More specifically, the two spool lands 94 and 95 are received withinthe valve body 96 and are connected to each other by an interconnectingstem 99 of reduced cross-sectional size such that the spool lands aremovable together in response to engine speed and load variations, aswill be described. The spool lands 94 and 95 are respectively positionedgenerally in axial alignment with a pair of radially enlarged annularoutlet chambers 100 and 102 which communicate respectively with theoutlet conduits 97 and 98. The spool lands are sized to close theseoutlet chambers, as viewed in FIG. 2, and are positioned normally in theclosed position by a spring-loaded position adjustment assembly 104reacting between the outboard axial side of the spool land 94 and theadjacent end wall 106 of the valve body. In the embodiment shown, thisadjustment assembly 104 comprises a set screw 108 threadably receivedthrough the end wall 106 to adjustably bear against a flange 110, and acompression spring 112 reacts between the flange 110 and the adjacentoutboard side of the spool land 94. Conveniently a guide cylinder 114extends from the flange 110 into an axially centered counterbore 116 inthe spool 94 to maintain the components in the desired axial alignmentwith each other.

The flow conduit 72 is connected to the control valve 76 at a positiongenerally intermediate the length of the valve body 96 for coupling theflow output of the gear pump 68 into an annular volume 118 defined bythe axially open space surrounding the stem 99 between the two spoollands 94 and 95. Accordingly, the hydraulic pressure of this flow outputacts in opposite axial directions upon the two spool lands 94 and 95such that the lands do not displace axially in response to the hydraulicpressure within the annular volume 118.

The flow conduit portion 74' is also coupled to the control valve 76,but this conduit portion 74' is connected for admission of itsassociated hydraulic flow output into a pressure chamber 120 between thespool land 95 and the adjacent end wall 122 of the valve body.Accordingly, the hydraulic pressure of the fluid in the conduit portion74' reacts between the spool land 95 and the end wall 122 to urge bothspool lands 94 and 95 in an axial direction against the force of thecompression spring 112. Conveniently to permit use of a relativelylightweight spring 112 and thereby obtain accurate control over movementof the spool land, a portion of the force in the chamber 120 can beoffset by coupling the fluid in the pressure chamber 120 through a smallcentral bore 124 into the counterbore 116 formed in the opposite spool94.

In operation, the pressure of the hydraulic fluid coupled to thepressure chamber 120 acts against the outboard axial face of the spoolland 95 to urge the two spool lands 94 and 95 axially against thecompression spring 112. When the pressure in the pressure chamber 120reaches a sufficient magnitude, the spool land 94 begins to uncover itsassociated annular outlet chamber 100 to allow a portion of the flowoutput supplied by the gear pump 68 to bypass the check valve 80 andflow through the annular volume 118 to the outlet chamber 100. Thus, aportion of the flow output supplied by the gear pump 68 is unloaded ordisconnected from the pressure chamber 120 and further from the supplyconduit 62. Importantly, the degree of fluid unloading is controlled bythe compression spring 112 in a manner to maintain the fluid pressurewithin the pressure chamber 120 substantially constant. The unloadedportion of the flow output is discharged from the outlet chamber 100 tothe associated outlet conduit 97 for supply to the relatively lowpressure conduit 54.

The above-described operation of the control valve is furtherillustrated graphically in FIG. 4, which depicts the variation in totalflow output of the gear pumps 68 and 70 as a function of engine speed.More particularly, as noted hereinabove, the two positive displacementgear pumps 68 and 70 driven by the engine provide a combined totalhydraulic fluid flow output which increases progressively with increasesin engine speed, as illustrated by the line 170 in FIG. 4. Upon startingof the engine, both engine speed and pump speed increase from zero witha corresponding increase in the combined pump flow output and hydraulicpressure within the conduits coupled to the hydraulic turbine. Thiscombined hydraulic pressure is communicated to the pressure chamber 120within the control valve 76. When the hydraulic pressure in the pressurechamber 120 reaches a predetermined selected magnitude, such as about1000 psi at about 1400 rpm pump speed, as illustrated by the dotted line172, the fluid pressure moves the spool lands 94 and 95 to beginunloading of the fluid output provided by the gear pump 68 to hold thepressure at a substantially constant level.

As engine and pump speed increase further, the combined flow output ofthe two gear pumps 68 and 70 also increase such that the control valve76 is required to increase the portion of hydraulic fluid unloaded fromthe supply conduit 62. In this regard, the spool lands 94 and 95 movefurther against the compression spring 112 to progressively increase theunloading of the fluid output of the gear pump 68 until the pump 68 isfully unloaded, as indicated by the region "A" of the line 172 in FIG.4. When this occurs, the other gear pump 70 is providing a sufficienthydraulic fluid flow output to maintain the pressure within the supplyconduit 62 at the desired selected magnitude, as shown by the line 174in FIG. 4, indicating the speed-responsive fluid flow rate provided bythe pump 70. However, with still further increases in engine and pumpspeed up to an arbitrary rated speed, as denoted by the speed line 176,the spool land 95 progressively uncovers its associated annular outletchamber 102 to progressively unload the fluid output of the pump 70through the outlet conduit 98 to the conduit 54 to maintain the pressurein the supply conduit 62 at the substantially constant level.

When engine speed subsequently decreases, the hydraulic fluid flow rateprogressively decreases to permit the spool lands 94 and 95 to movetoward their original positions under the influence of the compressionspring 112. As a result, the flow output of the gear pump 70 isprogressively reconnected to the supply conduit 62 followed by similarprogressive reconnection of the flow output of the gear pump 68 to theextent required for supplemental driving of the turbocharger.

The control valve 76 thus permits optimum supplemental driving of theturbocharger throughout a relatively low engine speed range, inclusiveof starting speeds, by coupling the total combined fluid flow output ofthe pumps 68 and 70 to the hydraulic turbine 58 until the fluid pressurein the supply conduit 62 reaches the predetermined magnitude. When thepredetermined pressure is reached, the control valve 76 functions tomaintain the pressure substantially constant with further increases inengine speed by progressively unloading the pump flow outputs. Since theenergy level in the engine exhaust gases increases with engine speed,this results in a relatively reduced supplemental driving of theturbocharger as engine speed increases. Importantly, the unloadedportions of the pump flow outputs are coupled to the low pressureconduit 54 such that the pumps are partially unloaded and can becontinuously operated without high power consumption. The low pressureconduit 54 recycles the unloaded fluid outputs to the small sump 69 atthe intake side of the pumps 68 and 70 for resupply to the pumps.

The control valve 76 further includes means for adjusting the positionof the spool lands 94 and 95 as a function of engine load. Morespecifically, a pneumatically operated actuator rod 130 is provided foradjustably varying the position of the spool lands in response to thepressure of the charge air supplied to the engine, wherein this chargeair pressure is representative of engine load.

The pneumatic adjustment means comprises, as viewed in FIG. 2, anenlarged housing 132 at the end of the valve body 96 adjacent thepressure chamber 120, wherein this housing is divided by a resilientdiaphragm 134 into a pair of axially separate chambers 136 and 138. Thechamber 136 is coupled to a low reference pressure, such as a connectionvia a conduit 140 to the sump return conduit 56, whereas the otherchamber 138 is coupled to charge air pressure as by a pneumatic line 142connected to the discharge side of the turbocharger compressor housing24. The diaphragm 134 is thus subjected to a pressure differentialindicative of engine load for movement axially toward the spool lands 94and 95.

The actuator rod 130 is suitably connected to the diaphragm 134, as byuse of retainer plates 144, and extends through a small bore 146 in thevalve body end wall 122 into the pressure chamber 120. While theactuator rod 130 can be physically connected to the adjacent spool land95, it is preferred to provide a normal spacing between the rod and landsuch that the control valve is capable of normal speed-responsiveoperation substantially independent of engine load. However, as engineload increases, the actuator rod 130 moves toward and eventually bearsagainst the outboard side of the spool land 95 to urge the spool lands94 and 95 toward a further unloaded position. This results in areduction in the pressure of the hydraulic fluid supplied to thehydraulic turbine 58 and thus also reduces the relative degree ofsupplemental driving of the turbocharger. Of course, when engine loaddecreases, the pneumatic pressure in the diaphragm chamber 138 decreasesto retract the actuator rod from engagement with the spool land 95 andpermit continued control valve operation solely in response to enginespeed. Conveniently, however, the pneumatic line 142 includes a flowrestrictor 145 to isolate the diaphragm from immediate response tocharge air pressure fluctuations of short duration.

When the engine load reaches a predetermined maximum level, the actuatorrod 130 couples a portion of the fluid in the pressure chamber 120 tothe shut-off valve 82 to insure positive closure of the shut-off valveand a cessation of supply of hydraulic fluid to the nonventilatedhydraulic turbine. More specifically, the actuator rod 130 includes anannular recess 148 which ultimately moves into communication with thepressure chamber 120 when the predetermined maximum load is reached.When this occurs, the fluid in the pressure chamber 120 is coupled to acontrol conduit 150 which is connected to the shut-off valve 82 into achamber 152 (FIG. 3) at the side of the piston 86 opposite the valveplug 90. This results in balanced fluid pressures acting on the piston86 to permit the spring 88 to positively seat the valve plug 90 on thevalve seat 92, with the fluid being exhausted from the chamber 152through a conduit 154 including a restrictor 156 to the low pressure oilsupply conduit 54. Fluid supply to the hydraulic turbine 58 is thuspositively prevented until the engine load decreases and the actuatorrod 130 moves the recess 148 out of communication with the pressurechamber 120. During cessation of fluid supply to the hydraulic turbine,turbocharger operation continues solely in response to engine exhaustgases.

The control arrangement of this invention thus accurately controls andschedules the flow rate and pressure of hydraulic fluid to an hydraulicassist turbocharger as a combined function of engine speed and load. Thecontrol arrangement regulates the hydraulic fluid flow to provide therequired level of supplemental turbocharger driving. The various pumpingelements of the control arrangement advantageously continue pumpingoperation for all conditions of engine operation to permit rapid supplyof the required hydraulic flow to the turbocharger. However, the pumpingelements are substantially unloaded one by one such that the individualpumping elements consume little power during continued operation whentheir outputs are disconnected from the turbocharger.

The control arrangement is particularly useful either with four-cycle ortwo-cycle engines, such as diesel engines, to provide supplementalturbocharger driving in response to engine speed and load. In atwo-cycle engine, the control arrangement is particularly advantageousin that the control valve can be scheduled for supplemental turbochargerdriving in a manner to eliminate any requirement for a conventionalscavenging blower. Moreover, the provision of the small sump 69 at theintake side of the pump assembly 60 permits a sufficient quantity ofhydraulic fluid to be circulated to the turbocharger during starting toaccelerate the turbocharger for providing sufficient charge air forstarting purposes. Thus, auxiliary starting equipment is not required.

A modified form of the hydropneumatic control valve for use in thecontrol arrangement 16 of this invention is illustrated in FIG. 5,wherein components identical to those shown and described with respectto FIG. 2 are designated by use of common reference numerals. Thismodified control valve 276 includes transient response means in additionto the speed- and load-responsive components for enabling a temporaryboosting of supplemental turbocharger driving during a transientoperating condition, such as a heavy acceleration.

As shown in FIG. 5, the modified control valve 276 includes the valvebody 96 in which is carried the spool lands 94 and 95 forspeed-responsive unloading of the fluid outputs provided by the two gearpumps. In addition, the control valve 276 includes the actuator rod 130carried by the resilient diaphragm 134 for load-responsive movement tofurther unload the pump fluid outputs to further reduce supplementalturbocharger driving, all as described with respect to the embodimentshown in FIG. 2. The speed- and load-responsive unloading of the fluidoutputs is opposed by the position adjustment assembly 104, includingthe compression spring 112, reacting between the spool land 94 and apiston flange 110 with an adjustment set screw 108 bearing against theoutboard side of the piston flange 110.

In the embodiment of FIG. 5, a transient response override valve 200 isprovided for sensing the occurrence of a predetermined transientcondition and for responding thereto to supply pressurized hydraulicfluid into the valve body 96 within a chamber 202 at the outboard sideof the piston flange 110. This provides an axial force supplementing theforce of the compression spring 112 and acting against the hydraulicpressure in the pressure chamber 120 to urge the spool lands 94 and 95toward a position of decreasing unloading. As a result, the fluidpressure within the pressure chamber 120 and supplied to the hydraulicturbine 58 is increased for the duration of the transient condition toincrease the level of supplemental driving of the turbocharger.

The transient response override valve 200 comprises, in a preferredform, a two-position solenoid valve assembly of conventionalconstruction responsive to the presence of a transient condition, suchas a heavy engine acceleration. This transient response can be achievedby use of conventional electronic fuel controls and scheduling devices,referred to generally by reference numeral 204, which provide anelectrical signal over conductors 206 to control energization of thesolenoid valve assembly 200.

During a transient condition, the solenoid valve assembly 200 isenergized to open a flow path between an appropriate supply of hydraulicfluid having at least a minimum pressure level and the override chamber202 within the valve body 96. As illustrated, the supply of hydraulicfluid can be obtained via a conduit 208 coupled to the fluid outletconduit 98 carrying fluid from the pressure chamber 120, although othersources of hydraulic fluid are available within the turbocharger system.When the transient condition ends, the solenoid valve assembly isdeenergized to close the conduit 208 and exhaust the override chamber,as by a drain conduit 210 coupled to the oil return conduit 56 or thelike. Conveniently, any fluid leaking past the piston flange 110 is alsodrained to the oil return conduit 56 by an additional drain conduit 212.

The modified control valve 276 thus permits supply of hydraulic fluid tothe hydraulic turbine 58 at a selected higher pressure level fortemporary increased supplemental turbocharger driving during a heavyacceleration condition. With this additional response characteristic,the compression spring 112 can be chosen to provide a smaller springforce than is required in the embodiment of FIG. 2 to provide a slightlyreduced constant pressure of hydraulic fluid over the major portion ofthe speed range, as depicted by the dot-dash line 214 in FIG. 4. Thisresults in a reduced supplemental driving of the turbocharger duringnontransient conditions without any adverse performance effect, sinceincreased supplemental driving is available during the transientcondition when the increased driving is required. That is, when thetransient condition is sensed, the control valve 276 decreases theunloading of the fluid outputs to increase the pressure of hydraulicfluid supplied to the hydraulic turbine to a higher level, as depictedby the dot-dash line 216 in FIG. 4. Of course, when the transientcondition concludes, the hydraulic pressure returns to the lower levelindicated by the line 214.

A variety of modifications and improvements to the control arrangementdescribed herein are believed to be apparent to one skilled in the art.Accordingly, no limitation on the invention is intended, except as setforth in the appended claims.

What is claimed is:
 1. For use in a turbocharged engine including anhydraulic assist turbocharger having an exhaust gas driven turbine forrotatably driving a compressor, and an hydraulic turbine forsupplementally driving the compressor, a control arrangement forcontrolling the supply of hydraulic fluid to the hydraulic turbine forrotatably driving the hydraulic turbine, comprising:a pump assemblyincluding a plurality of pumping elements for providing a plurality ofhydraulic flow outputs for supply to the hydraulic turbine; and controlvalve means including means for responding to engine speed and means forresponding to engine load for coupling the hydraulic flow outputs to thehydraulic turbine during one condition of engine operation for maximumsupplemental driving of the compressor, and for serially andprogressively uncoupling the hydraulic flow outputs from the hydraulicturbine one at a time in response to changes in at least one of enginespeed and load indicative of a requirement for reduced supplementaldriving of the compressor.
 2. The control arrangement of claim 1 whereinsaid plurality of pumping elements comprise a plurality of positivedisplacement pumping elements.
 3. The control arrangement of claim 1wherein said plurality of pumping elements comprise a plurality ofengine driven gear pumps.
 4. The control arrangement of claim 1including means for combining the separate hydraulic outputs of saidpumping elements for supply as a single hydraulic flow to the hydraulicturbine.
 5. The control arrangement of claim 1 wherein said controlvalve means progressively uncouples the hydraulic flow outputs one at atime from the hydraulic turbine in response to changes in at least oneof engine speed and load indicative of a requirement for reducedsupplemental driving of the compressor.
 6. The control arrangement ofclaim 1 wherein said speed-responsive means is responsive to enginespeed for coupling the hydraulic flow outputs to the hydraulic turbinewhen engine speed is relatively low and for serially uncoupling thehydraulic flow outputs from the hydraulic turbine in response toincreases in engine speed.
 7. The control arrangement of claim 6 whereinsaid pump assembly includes a pair of pumping elements, and wherein saidspeed responsive means is responsive to engine speed for progressivelyuncoupling the hydraulic flow output of one of said pumping elements andthen progressively uncoupling at least partially the hydraulic flowoutput of the other of said pumping elements.
 8. The control arrangementof claim 1 wherein said lead-responsive means is responsive to engineload for coupling the hydraulic flow outputs to the hydraulic turbinewhen engine load is relatively low and for serially uncoupling thehydraulic flow outputs from the hydraulic turbine in response toincreases in engine load.
 9. The control arrangement of claim 1including shut-off valve means responsive to at least one of enginespeed and load for positively preventing flow of hydraulic fluid to thehydraulic turbine during a second condition of engine operation.
 10. Thecontrol arrangement of claim 1 wherein said speed-responsive means andsaid load-responsive means are responsive to a predetermined function ofengine speed and load for coupling the hydraulic flow outputs to thehydraulic turbine when said function is indicative of said one conditionof engine operation and for serially uncoupling said hydraulic flowoutputs from the hydraulic turbine when said function is indicative of areduced requirement for supplemental driving of the compressor.
 11. Thecontrol arrangement of claim 10 wherein said speed-responsive means andsaid load-responsive means serially uncouples the hydraulic flow outputsfrom the hydraulic turbine in response to increases in engine speed andin response to increases in engine load.
 12. The control arrangement ofclaim 10 including means responsive to engine load for positivelypreventing flow of hydraulic fluid to the hydraulic turbine when engineload reaches a predetermined magnitude.
 13. The control arrangement ofclaim 1 wherein said control valve means includes means for couplingsaid hydraulic flow outputs when uncoupled from the hydraulic turbine toa relatively low pressure sump for substantially unloading saidassociated pumping element in response to changes in at least one ofengine speed and load indicative of a reduced requirement forsupplemental driving of the compressor.
 14. The control arrangement ofclaim 1 wherein said plurality of pumping elements comprises first andsecond engine-driven gear pumps; and wherein said control valve meanscomprises a spool valve having a hollow valve body with a pair ofdischarge outlets, a pair of spool lands carried within said valve bodyand connected together for simultaneous axial sliding movement,adjustable spring means for urging said spool lands to a normal positioncovering said discharge outlets, and means for coupling the flow outputof said first gear pump into said valve body between said spool landsand for coupling the flow output of at least said second gear pump intosaid valve body for urging said spool lands axially against said springmeans to progressively uncover one of said discharge outlets forprogressively uncoupling the flow output of said first gear pump fromthe hydraulic turbine and then to progressively uncover the other ofsaid discharge outlets for progressively uncoupling at least partiallythe flow output of said second gear pump from the hydraulic turbine. 15.The control arrangement of claim 14 including means for combining theflow outputs of said first and second gear pumps for supply as acombined flow to the hydraulic turbine, and wherein said means forcoupling the flow output of at least said second gear pump to said valvebody comprises means for coupling the combined flow to said valve body.16. The control arrangement of claim 14 including an actuator roddisposed for axially bearing engagement with one of said spool lands,and means for urging said rod in an axial direction for bearingengagement with said one spool land to urge said spool lands againstsaid spring means in response to increasing engine load.
 17. The controlarrangement of claim 16 wherein said urging means comprises a flexiblediaphragm movably responsive to the pressure of air discharged from thecompressor for moving said actuator rod axially with respect to saidspool lands.
 18. For use in a turbocharged engine system including anhydraulic assist turbocharger having an exhaust gas driven turbine forrotatably driving a compressor, and an hydraulic turbine forsupplementally driving the compressor, a control arrangement forcontrolling the supply of hydraulic fluid to the hydraulic turbine forrotatably driving the hydraulic turbine, comprising:a plurality ofpositive displacement pumping elements driven by the engine to provide aplurality of hydraulic output flows each having a flow rate directlyproportional to engine speed; and control valve means for responding tothe flow rates of said hydraulic flow outputs for coupling said flowoutputs to the hydraulic turbine for maximum supplemental driving of thecompressor when engine speed is relatively low, and for serially andprogressively uncoupling said flow outputs from the hydraulic turbineupon increases in engine speed to maintain the pressure of hydraulicfluid supplied to the hydraulic turbine substantially constantthroughout a range of increasing engine speed for progressivelyrelatively reduced supplemental driving of the compressor; said controlvalve means further including transient response means for responding tothe presence of a transient engine operating condition for increasingthe pressure of the hydraulic fluid supplied to the hydraulic turbinefor the duration of the sensed transient condition.
 19. The controlarrangement of claim 18 including means for combining said flow outputsinto a combined hydraulic flow for supply through a supply conduit tothe hydraulic turbine, said control valve means being responsive to thepressure of hydraulic fluid in said supply conduit for seriallyuncoupling said flow outputs.
 20. The control arrangement of claim 18wherein said control valve means further includes means forprogressively reducing the pressure of the hydraulic fluid supplied tothe hydraulic turbine in response to increases in engine load.
 21. Thecontrol arrangement of claim 20 including shut-off valve meansresponsive to engine load for positively preventing flow of hydraulicfluid to the hydraulic turbine when engine load reaches a predeterminedmagnitude.
 22. The control arrangement of claim 18 wherein said controlvalve means includes means for coupling the uncoupled flow outputs to arelatively low pressure sump for substantially unloading said associatedpumping elements.
 23. For use in a turbocharged engine system includingan hydraulic assist turbocharger having an exhaust gas driven turbinefor rotatably driving a compressor, and an hydraulic turbine forsupplementally driving the compressor, a control arrangement forcontrolling the supply of hydraulic fluid to the hydraulic turbine forrotatably driving the hydraulic turbine, comprising:a plurality ofpumping elements for providing a plurality of hydraulic flow outputs forsupply to the hydraulic turbine; and control means for responding toengine load for coupling the hydraulic flow outputs to the hydraulicturbine when engine load is relatively low for maximum supplementaldriving of the compressor, and for serially and progressively uncouplingthe hydraulic flow outputs from the hydraulic turbine in response toincreases in engine load for reduced supplemental driving of thecompressor; said control valve means further including transientresponse means for sensing the presence of a transient engine operatingcondition and for increasing the pressure of the hydraulic fluidsupplied to the hydraulic turbine for the duration of the sensedtransient condition.
 24. The control arrangement of claim 23 includingshut-off valve means responsive to engine load for positively preventingflow of hydraulic fluid to the hydraulic turbine when engine loadreaches a predetermined magnitude.
 25. The control arrangement of claim23 wherein said control valve means includes means for coupling theuncoupled flow outputs to a relatively low pressure sump forsubstantially unloading said associated pumping elements.
 26. Thecontrol arrangement of claim 23 wherein said pumping elements comprise aplurality of positive displacement pumping elements driven at a speeddirectly proportional to engine speed, said control valve meansincluding a valve member movably responsive to the pressure of saidhydraulic flow outputs for progressively uncoupling said flow outputsfrom the hydraulic turbine one at a time in response to increases inengine speed to maintain the pressure of the hydraulic fluid supplied tothe hydraulic turbine relatively constant throughout a range of enginespeeds, said control valve means further including means responsive toengine load for adjusting the position of said valve member to decreasethe pressure of the hydraulic fluid supplied to the hydraulic turbine inresponse to increases in engine load.
 27. The control arrangement ofclaim 26 wherein said load-responsive means includes means responsive tothe pressure of air discharged from the compressor for bearing againstsaid valve member when said air pressure is relatively high for movingsaid valve member toward a position further uncoupling said flow outputsfrom the hydraulic turbine.
 28. For use in a turbocharged engine systemincluding an hydraulic assist turbocharger having an exhaust gas driventurbine for rotatably driving a compressor, and an hydraulic turbine forsupplementally driving the compressor, a control arrangement forcontrolling the supply of hydraulic fluid to the hydraulic turbine forrotatably driving the hydraulic turbine, comprising:a plurality ofpositive displacement pumping elements driven by the engine to provide aplurality of hydraulic flow outputs each having a flow rate directlyproportional to engine speed; means for combining said flow outputs intoa combined flow for supply to the hydraulic turbine; and control valvemeans including first means responsive to the hydraulic pressure of saidcombined flow for serially and progressively uncoupling said flowoutputs one at a time from said combined flow upon increases in enginespeed to maintain the pressure of the hydraulic fluid supplied to thehydraulic turbine substantially constant throughout a range of enginespeeds to reduce the relative level of supplemental driving of thecompressor upon increases in engine speed, and second means responsiveto the pneumatic pressure of air discharged from the compressor foradjusting the position of said first means to further serially andprogressively uncouple said flow outputs one at a time from saidcombined flow upon increases in said pneumatic pressure to reducefurther the relative level of supplemental driving of the compressorthroughout a range of relatively high pneumatic pressures.
 29. Thecontrol arrangement of claim 28 including shut-off valve meansresponsive to engine load for positively preventing flow of hydraulicfluid to the hydraulic turbine when engine load reaches a predeterminedmagnitude.
 30. The control arrangement of claim 29 wherein said shut-offvalve means comprises a valve member in association with said combinedflow and movable to a position preventing supply of any portion of saidcombined flow to the hydraulic turbine, said valve member having acontrol chamber formed therein and being responsive to supply of a fluidunder pressure to said control chamber for preventing supply ofhydraulic fluid to the hydraulic turbine, said control valve meansincluding means for coupling a portion of the combined flow to saidcontrol chamber when said pneumatic pressure reaches a predeterminedmagnitude.
 31. The control arrangement of claim 28 wherein said controlvalve means further includes transient response means for sensing thepresence of a transient engine operating condition and for adjusting theposition of said first means to decrease unloading of the hydraulic flowoutputs for the duration of the sensed transient condition.
 32. For usein a turbocharged engine system including an hydraulic assistturbocharger having an exhaust gas driven turbine for rotatably drivinga compressor, and an hydraulic turbine for supplementally driving thecompressor, a control arrangement for controlling the supply ofhydraulic fluid to the hydraulic turbine for rotatably driving thehydraulic turbine, comprising:a plurality of positive displacementpumping elements driven by the engine to provide a plurality ofhydraulic flow outputs each having a flow rate directly proportional toengine speed; means for combining said flow outputs into a combined flowfor supply to the hydraulic turbine; and control valve means includingfirst means responsive to the hydraulic pressure of said combined flowfor serially and progressively uncoupling said flow outputs one at atime from said combined flow upon increases in engine speed to maintainthe pressure of the hydraulic fluid supplied to the hydraulic turbinesubstantially constant throughout a range of engine speeds to reduce therelative level of supplemental driving of the compressor upon increasesin engine speed, second means responsive to the pneumatic pressure ofair discharged from the compressor for adjusting the position of saidfirst means to further serially and progressively uncouple said flowoutputs one at a time from said combined flow upon increases in saidpneumatic pressure to reduce further the relative level of supplementaldriving of the compressor throughout a range of relatively highpneumatic pressures, and transient response means for sensing thepresence of a transient engine operating condition and for adjusting theposition of said first means to decrease unloading of the hydraulic flowoutputs for the duration of the sensed transient condition.
 33. Thecontrol arrangement of claim 32 wherein said first means comprises avalve member movable in response to the pressure of the hydraulic fluidsupplied to the hydraulic turbine, said second means and said transientresponse means being for adjusting the position of said valve member.34. The control arrangement of claim 32 wherein said first meanscomprises a valve member movable in one direction for serially andprogressively uncoupling the flow outputs one at a time from thehydraulic turbine and spring means for biasing said valve member in adirection opposite said one direction, said second means including meansfor overriding said spring means in response to increases in engine loadfor moving said valve member in said one direction, and said transientresponse means including means for supplementing said spring means andfor overriding said second means for moving said valve member in saidopposite direction.
 35. For use in a turbocharged engine systemincluding an hydraulic assist turbocharger having an exhaust gas driventurbine for rotatably driving a compressor and an hydraulic turbine forsupplementally driving the compressor, a control arrangement forcontrolling the supply of hydraulic fluid to the hydraulic turbine forrotatably driving the hydraulic turbine, comprising:a pump assemblyincluding a plurality of pumping elements for providing a plurality ofhydraulic flow outputs for supply to the hydraulic turbine; and controlvalve means for coupling the hydraulic flow outputs to the hydraulicturbine, said control valve means including first means for limiting thepressure of hydraulic fluid supplied to the hydraulic turbine to asubstantially constant pressure level throughout a range of enginespeeds, said first means including means for progressively unloading thehydraulic flow outputs one at a time from the hydraulic turbine inresponse to increases in engine speed, and second means for overridingsaid first means and for reducing the pressure of hydraulic fluidsupplied to the hydraulic turbine in response to relatively high levelsof engine load, said second means including means for adjusting theposition of said first means for further unloading of the hydraulic flowoutputs in response to increases in engine load.
 36. The controlarrangement of claim 35 further including transient response means forsensing the presence of a transient engine operating condition and foradjusting the position of said first means to decrease unloading of thehydraulic flow outputs for the duration of the sensed transientcondition.
 37. For use in a turbocharged engine system including anhydraulic assist turbocharger having an exhaust gas driven turbine forrotatably driving a compressor, and an hydraulic turbine forsupplementally driving the compressor, a control arrangement forcontrolling the supply of hydraulic fluid to the hydraulic turbine forrotatably driving the hydraulic turbine, comprising:a pump assemblyincluding a plurality of pumping elements for providing a plurality ofhydraulic flow outputs for supply to the hydraulic turbine; and controlvalve means including first means for limiting the pressure of hydraulicfluid supplied to the hydraulic turbine to a substantially constantpressure level throughout a range of engine speeds, second means foroverriding said first means and for reducing the pressure of hydraulicfluid supplied to the hydraulic turbine in response to increases inengine load throughout a range of engine loads, and third means forresponding to the presence of a transient engine operating condition foroverriding said first and second means and for increasing the pressureof the hydraulic fluid supplied to the hydraulic turbine for theduration of the sensed transient condition.
 38. For use in aturbocharged engine system including an hydraulic assist turbochargerhaving an exhaust gas driven turbine for rotatably driving a compressor,and an hydraulic turbine for supplementally driving the compressor, acontrol arrangement for controlling the supply of hydraulic fluid to thehydraulic turbine for rotatably driving the hydraulic turbine,comprising:a plurality of positive displacement pumping elements drivenby the engine to provide a plurality of hydraulic output flows eachhaving a flow rate directly proportional to engine speed; and controlvalve means including first means for responding to the flow rates ofsaid hydraulic flow outputs for coupling said flow outputs to thehydraulic turbine for maximum supplemental driving of the compressorwhen engine speed is relatively low and for serially and progressivelyuncoupling said flow outputs from the hydraulic turbine upon increasesin engine speed to maintain the pressure of hydraulic fluid supplied tothe hydraulic turbine substantially constant throughout a range ofincreasing engine speed for progressively relatively reducedsupplemental driving of the compressor, second means for progressivelyreducing the pressure of the hydraulic fluid supplied to the hydraulicturbine in response to increases in engine load, and transient responsemeans for responding to the presence of a transient engine operatingcondition for increasing the pressure of the hydraulic fluid supplied tothe hydraulic turbine for the duration of the sensed transientcondition.
 39. For use in a turbocharged engine system including anhydraulic assist turbocharger having an exhaust gas driven turbine forrotatably driving a compressor, and an hydraulic turbine forsupplementally driving the compressor, a control arrangement forcontrolling the supply of hydraulic fluid to the hydraulic turbine forrotatably driving the hydraulic turbine, comprising:a plurality ofpositive displacement pumping elements driven at a speed directlyproportional to engine speed for providing a plurality of hydraulic flowoutputs for supply to the hydraulic turbine; and control valve meansincluding a valve member for movably responding to the pressure of saidhydraulic flow outputs for progressively uncoupling said flow outputsfrom the hydraulic turbine one at a time in response to increases inengine speed to maintain the pressure of the hydraulic fluid supplied tothe hydraulic turbine relatively constant throughout a range of enginespeeds, said valve member being further for movably responding to engineload for coupling the hydraulic flow outputs to the hydraulic turbinewhen engine load is relatively low for maximum supplemental driving ofthe compressor, and for serially and progressively uncoupling thehydraulic flow outputs from the hydraulic turbine in response toincreases in engine load for reduced supplemental driving of thecompressor, said control valve means further including transientresponse means for sensing the presence of a transient engine operatingcondition and for adjusting the position of said valve member forincreasing the pressure of the hydraulic fluid supplied to the hydraulicturbine for the duration of the sensed transient condition.
 40. For usein a turbocharged engine system including an hydraulic assistturbocharger having an exhaust gas driven turbine for rotatably drivinga compressor, and an hydraulic turbine for supplementally driving thecompressor, a control arrangement for controlling the supply ofhydraulic fluid to the hydraulic turbine for rotatably driving thehydraulic turbine, comprising:a plurality of pumping elements couplingfirst and second engine-driven gear pumps for providing a plurality ofhydraulic flow outputs for supply to the hydraulic turbine; and controlvalve means for responding to engine load for coupling the hydraulicflow outputs to the hydraulic turbine when engine load is relatively lowfor maximum supplemental driving of the compressor, and for serially andprogressively uncoupling the hydraulic flow outputs from the hydraulicturbine in response to increases in engine load for reduced supplementaldriving of the compressor; said control valve means comprising a spoolvalve having a hollow valve body with a pair of discharge outlets, apair of spool lands carried within said valve body and connectedtogether for simultaneous axial sliding movement, spring means forurging said spool lands to a normal position covering said dischargeoutlets, means for coupling the flow output of said first gear pump intosaid valve body between said spool lands and for coupling the flowoutput of at least said second gear pump into said valve body for urgingsaid spool lands axially against said spring means to progressivelyuncover one of said discharge outlets for progressively uncoupling theflow output of said first gear pump from the hydraulic turbine and thento progressively uncover the other of said discharge outlets forprogressively uncoupling at least partially the flow output of saidsecond gear pump from the hydraulic turbine, an actuator rod disposedfor axially bearing engagement with one of said spool lands, and meansfor urging said rod in an axial direction for bearing engagement withsaid one spool land to urge said spool lands against said spring meansin response to increasing engine load.
 41. The control arrangement ofclaim 40 wherein said urging means comprises a flexible diaphragmmovably responsive to the pressure of air discharged from the compressorfor moving said actuator rod axially with respect to said spool lands.